function my_custom_subscriptions_init() {

    $args = array(
        'numberposts' => 10,
        'post_type'   => 'shop_subscription',
        'post_status' => 'any',
        'fields'      => 'ids',
        'order'       => 'ASC',
    );

    $subscriptions = get_posts( $args );

    wpf_log( 'info', 0, 'Beginning <strong>WooCommerce Subscription Meta</strong> batch operation on ' . count( $subscriptions ) . ' subscriptions', array( 'source' => 'batch-process' ) );

    return $subscriptions;

}

add_filter( 'wpf_batch_woo_subscriptions_meta_init', 'my_custom_subscriptions_init', 20 );